The geographic footprint of host-symbiont mutualism

宿主-共生体互利共生的地理足迹

• 批准号: 2208857
• 负责人: Thomas Miller
• 金额: $ 87.5万
• 依托单位: William Marsh Rice University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2022
• 资助国家: 美国
• 起止时间: 2022-07-15 至 2026-06-30
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2208857&HistoricalAwards=false
• 关键词: geographic; footprint; host; symbiont; mutualism

Every species on Earth has limits to its geographic distribution – places on the planet where it cannot live. Studying how range limits arise is important because it helps people understand where species such as pests or disease vectors are likely or unlikely to be found, and whether species might be able to migrate as environments change. It is generally accepted that, approaching the edges of a species’ distribution, stress from harshness of the environment eventually causes the death rate to exceed the birth rate, so that populations cannot sustain themselves. This generates a range edge. However, many plants and animals harbor a rich array of microbes that live inside of themselves, and these microbes (collectively called the microbiome) may help to ameliorate stress. This leads to the hypothesis that, by helping hosts deal with stress, microbes may alter the limits of a species’ distribution. The proposed research will test this hypothesis using plants that live symbiotically with microscopic fungi. The fungi are known elsewhere to help the plants cope with drought stress. The researchers will remove fungal symbionts from some plants and leave them in others, then place both plant types out into experimental plots that span the wet core to the dry edge of the plant species’ distributions. They will do this experiment for three grass species important to rangeland productivity. Data from this experiment will be used to build mathematical models that reveal how the fungal microbes affect the balance of birth and death rates in the host plants near and away from their range edges. This will help us understand the importance of plant-microbe symbioses as climate changes. Fungal symbionts are passed from adult plants through seeds. The researchers will thus visit herbaria, which are museums of stored plant collections, to extract fungi from seeds of stored grasses over the last 100 years to test how the plant-fungal interactions have changed through time. The project is designed to build connections between the study of plant microbiomes and the study of species’ distributions, which historically have had little cross-talk. Understanding the processes that generate limits on species’ geographic distributions is a classic problem in ecology that takes on urgency in the face of rapid environmental change. There is wide recognition that species interactions, together with abiotic forcing, may play a key role in shaping geographic distributions. However, current theory and data overwhelmingly focus on antagonistic interactions like consumption and competition. This project will test the influence of mutualism between host organisms and their microbial symbionts on the geographic distributions of both partners under current and future climate scenarios. Using a generalizable model system with a well-developed toolkit (cool-season grasses and their vertically-transmitted fungal endophytes), this project will combine geographically distributed symbiont removal experiments, demographic range modeling, climate change forecasting, collections-based surveys, and genetic profiling of symbionts to measure, for the first time, the geographic footprint of host-symbiont mutualism. Experiments will focus on three eastern North American grass species that meet their western limits along the dramatic aridity gradient of the south-central US, which is shifting under climate change. First, the research team will test competing hypotheses for the effect of symbiosis on host range limits, which depends on how symbionts influence host responses to abiotic (aridity) and biotic (herbivory) stress from range-core to range-edge. Mechanistic range models built with experimental data will quantify how symbionts modify host range limits via these two types of protection. Second, the team will quantify how context-dependent fitness effects scale up to influence clines in symbiont prevalence, which determine the symbiont geographic distribution. Finally, the research team will pursue greater spatial, temporal, and taxonomic coverage by sampling nine host species from herbarium specimens. Herbarium work will reconstruct geographic and temporal trends in the prevalence and fitness effects of endophytes across the central US to test how host-symbiont interactions have responded to rapid environmental change. Collectively, this work will advance mechanistic understanding of the origins of range limits and enhance the ability to forecast how species’ ranges will respond to future environmental change – among the most urgent priorities in population and community ecology.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

地球上的每个物种都有其地理分布的限制——研究其范围限制是如何产生的很重要，因为它可以帮助人们发现可能或不可能发现害虫或疾病媒介等物种，以及是否存在物种。人们普遍认为，在接近物种分布的边缘时，来自恶劣环境的压力最终会导致死亡率超过出生率，从而导致种群无法维持生存。然而，许多植物和动物都有栖息地。生活在其体内的大量微生物，这些微生物（统称为微生物组）可能有助于缓解压力，这导致了这样的假设：通过帮助宿主应对压力，微生物可能会改变物种分布的限制。拟议的研究将利用与微生物共生的植物来测试这一假设，这些真菌在其他地方已知可以帮助植物应对干旱胁迫，研究人员将从一些植物中去除真菌共生体，然后将其留在其他植物中。将这两种植物类型放置在横跨植物物种分布的湿核心到干边缘的实验田中，他们将对三种对牧场生产力很重要的草种进行这项实验，该实验的数据将用于建立数学模型。揭示真菌微生物如何影响靠近和远离其范围边缘的寄主植物的出生率和死亡率的平衡，这将有助于我们了解随着气候变化真菌共生体从成年植物通过种子传递的重要性。研究人员将因此，参观植物标本室，这是储存植物收藏的博物馆，从过去 100 年来储存的草种子中提取真菌，以测试植物与真菌的相互作用如何随着时间的推移而变化。该项目旨在建立植物研究之间的联系。微生物组和物种分布的研究在历史上几乎没有交叉，理解对物种地理分布产生限制的过程是生态学中的一个经典问题，在快速的环境变化面前显得尤为紧迫。承认该物种相互作用以及非生物强迫可能在塑造地理分布方面发挥关键作用，然而，当前的理论和数据绝大多数集中在消耗和竞争等对抗性相互作用上。该项目将使用具有完善工具包（冷季草及其垂直传播的真菌内生菌）的通用模型系统，结合地理分布的共生体去除。实验、人口范围建模、气候变化预测、基于收集的调查和共生体的遗传分析，首次测量宿主-共生体互利共生的地理足迹。实验将集中于北美东部三种符合其要求的草种。首先，研究小组将测试共生对寄主范围限制的影响的相互竞争的假设，这取决于共生体如何影响寄主的反应。从范围核心到范围边缘的非生物（干旱）和生物（食草）压力，利用实验数据构建的机械范围模型将量化共生体如何通过这两种类型的保护来改变宿主范围限制。依赖性适应性效应会扩大影响共生体流行程度，从而决定共生体的地理分布。最后，研究小组将通过从植物标本馆中采样九种宿主物种来追求更大的空间、时间和分类覆盖范围。这项工作将重建美国中部内生菌流行率和适应度影响的地理和时间趋势，以测试宿主-共生体相互作用如何应对快速的环境变化。总的来说，这项工作将促进对范围限制起源的机械理解，并增强对范围限制的认识。预测物种分布范围将如何应对未来环境变化的能力——这是人口和社区生态学中最紧迫的优先事项之一。该奖项反映了 NSF 的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。

项目成果

The geographic footprint of mutualism: How mutualists influence species' range limits

互利共生的地理足迹：互利共生如何影响物种的范围限制

• DOI: 10.1002/ecm.1558
• 发表时间: 2023-01
• 期刊: Ecological Monographs
• 影响因子: 6.1
• 作者: Fowler, Joshua C.;Donald, Marion L.;Bronstein, Judith L.;Miller, Tom E. X.
• 通讯作者: Miller, Tom E. X.